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Synthesis of arylamines
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Iridium complexes bearing an N-heterocyclic carbene (NHC) ligand exhibited
high catalytic performance for the N-methylation of both aliphatic and
aromatic primary amines using methanol as the methylating agent. For aliphatic
amines, selective N,N-dimethylation was achieved at low temperatures. For
aromatic amines, selective N-monomethylation and selective N,N-dimethylation
were accomplished.
G. Toyooka, A. Tuji, K.-i. Fujita, Synthesis, 2018, 50,
4617-4626.
A Cp*Ir complex bearing a functional 2,2′-bibenzimidazole ligand is a highly
effective and general catalyst for the N-methylation of a variety of
amines with methanol in the presence of a weak base.
R. Liang, S. Li, R. Wang, L. Lu, F. Li, Org. Lett.,
2017, 19, 5790-5793.
[(p-cymene)Ru(2,2'-bpyO)(H2O)] is a general and efficient
catalyst for the N-methylation of amines and sulfonamides with methanol
in the presence of a carbonate salt. The reaction tolerates a series of
sensitive substituents, such as nitro, ester, cyano, and vinyl groups.
P. Liu, N. T. Tung, X. Xu, J. Yang, F. Li, J. Org. Chem., 2021, 86,
2621-2631.
Various aromatic amines were selectively methylated in the presence of MeOH and
KOtBu into their corresponding monomethylated secondary amines in high
yields at 150°C with very low loading of a PNHP-Pincer Ru
catalyst.
O. Ogata, H. Nara, M. Fujiwhara, K. Matsumura, Y. Kayaki, Org. Lett.,
2018, 20, 3866-3870.
Low loadings of an air-stable and easy to prepare Ru complex bearing a
tridentate redox-active azo-aromatic pincer ligand catalyze N-alkylation
of amines with C3-C10 alcohols. A wide array of N-methylated, N-ethylated,
and N-alkylated amines were prepared in good yields with wide functional
group tolerance.
A. K. Guin, S. Pal, S. Chakraborty, S. Chakraborty, N. D. Paul, J. Org. Chem., 2023, 88,
5944-5961.
A Chan-Lam coupling using methylboronic acid enables a selective monomethylation
of anilines. An incubation period of the substrate with the copper reagent is
needed before addition of the methylboronic acid. N-Methylanilines are
synthesized in good yields.
I. González, J. Mosquera, C. Guerrero, R. Rodríguez, Jacobo Cruces, Org. Lett., 2009,
11, 1677-1680.
A copper-catalyzed protocol for reductive methylation of amines and imine with
formic acid as a C1 source and phenylsilane as a reductant provides the
corresponding methylamines in good to excellent yields under mild conditions.
C. Qiao, X.-F. Liu, X. Liu, L.-N. He, Org. Lett.,
2017, 19, 1490-1493.
An iron(0) complex bearing a cyclopentadienone ligand catalyzes mild N-ethylation
and N-methylation of aryl and aliphatic amines with ethanol or methanol
in basic conditions through a hydrogen autotransfer borrowing process. A broad
range of aromatic and aliphatic amines underwent mono- or dialkylation in high
yields.
A. Lator, S. Gaillard, A. Poater, J.-L. Renau, Org. Lett.,
2018, 20, 5985-5990.
Well-defined Co(II) complexes stabilized by a PCP ligand catalyze efficient
alkylations of aromatic amines by primary alcohols into mono-N-alkylated
amines in very good yields. The inexpensive, earth-abundant nonprecious metal
catalysts make this acceptorless alcohol dehydrogenation concept environmentally
benign.
M. Mastalir, G. Tomsu, E. Pittenauer, G. Allmaier, K. Kirchner, Org. Lett.,
2016, 18, 3462-3465.
A radical-mediated decarboxylative C(sp3)-N cross-coupling of
diacyl peroxides with nitrogen nucleophiles, including indazoles, triazoles,
indoles, and anilines provides a broad range of alkylated products. The primary
and secondary alkyl radicals derived from corresponding diacyl peroxides were
generated by copper catalysis or by merging copper catalysis and photoredox
catalysis, respectively.
Z. -L. Tang, X.-H. Ouyang, R.-J. Song, J.-H. Li, Org. Lett., 2021, 23,
1000-1004.
At atmospheric pressure and at 130-160°C, primary aromatic amines are mono-N-alkylated
with a very high selectivity in a single step, with symmetrical and asymmetrical
dialkyl carbonates in the presence of a commercially available NaY faujasite. No
solvents are required.
M. Selva, P. Tundo, A. Perosa, J. Org. Chem., 2001,
66, 677-680.
In the presence of a catalytic amount of copper(II) acetate and di-tert-butyl
peroxide, a cross-coupling reaction of anilines with alkylborane reagents gives
N-alkylated anilines in good to excellent yields. Phenols are also
applicable for this reaction.
S. Sueki, Y. Kuninobu, Org. Lett., 2013,
15, 1544-1547.
An easy Pd-mediated oxidation of primary amines to imines followed by aniline
addition enables an alkylation of anilines. The process is characterized by a
high atom economy as ammonia is the only byproduct. The catalyst could be
successfully recycled up to three times.
P. Linciano, M. Pizzetti, A. Porcheddu, M. Taddei, Synlett, 2013, 24,
2249-2254.
A catalytic system generated in situ from a tetranuclear Ru-H complex with a
catechol ligand enables a direct deaminative coupling of two primary amines to
form secondary amines. The analogous coupling of aniline with primary amines
formed aryl-substituted secondary amines.
P. T. K. Arachchige, H. Lee, C. S. Yi, J. Org. Chem., 2018, 83,
4932-4947.
A catalytic amount of CuCl was used in combination with 4CzIPN as organic photoredox catalyst to
effect decarboxylative C(sp3)-N coupling. The reaction provides a variety of
alkyl amines from readily available alkyl carboxylic acids. The coupling worked
with both anilines and imines as nitrogen sources.
G. Barzanň, R. Mao, M. Garreau, J. Waser, X. Hu,
Org. Lett., 2020, 22, 5412-5416.
Commercially available [(PPh3)2NiCl2] is an
efficient catalyst for the mono-N-alkylation of (hetero)aromatic amines,
employing alcohols to deliver diverse secondary amines in excellent yields via
the borrowing hydrogen strategy. The catalyst system can also be used for
accessing various quinoline derivatives following the acceptorless
dehydrogenation pathway.
S. N. R. Donthireddy, V. K. Pandey, A. Rit, J. Org. Chem., 2021, 86,
6994-7001.
A monobenzylation of aromatic amines with benzylic alcohols in good yields
proceeds under MW conditions in the presence of SmI2 as a catalyst
with the generation of water as the sole byproduct. This reaction offers a broad
substrate scope and good functional-group tolerance.
J. Gour, S. Gatadi, S. Malasala, M. V. Yaddanpudi, S. Nanduri, J. Org. Chem., 2019, 84,
7488-7494.
A well-defined Zn(II)-complex catalyzes a sustainable and eco-friendly N-alkylation
of various amines by alcohols in very good yields. The method shows wide
functional group tolerance and produces the precursors in high yields for the
marketed drugs tripelennamine and thonzonium bromide in gram-scale reactions.
S. Chakraborty, R. Mondal, S. Pal, A. J. Guin, L. Roy, N. D. Paul, J. Org. Chem., 2023, 88,
771-787.
A base-catalyzed/promoted transition-metal-free direct alkylation of amines with
either aromatic or aliphatic alcohols provides the desired amines in good yields.
Q.-Q. Li, Z.-F. Xiao, C.-Z. Yao, H.-X. Zheng, Y.-B. Kang, Org. Lett.,
2015,
17, 5328-5331.
The addition of 4 Ĺ molecular sieves enables an efficient cobalt(II)-catalyzed
N-alkylation of both aromatic and aliphatic amines with alcohols with high
chemoselectivity (amines vs imines). A hydrogen-borrowing mechanism is
responsible for the tandem acceptorless dehydrogenation/condensation/hydrogenation
process.
G. Zhang, Z. Yin, S. Zheng, Org. Lett., 2016, 18,
300-303.
Copper N-heterocyclic carbene complexes serve as catalysts for both aerobic
oxidation of alcohols to aldehydes and reduction of imines to amines. A one-pot
tandem synthetic strategy affords useful secondary amines from benzylic alcohols
and anilines via an oxidation-reduction strategy.
L.-W. Zhan, L. Han, P. Xing, B. Jiang, Org. Lett.,
2015,
17, 5990-5993.
The [RuCl2(p-cymene)]2/Ph2SiH2
catalytic system is very efficient for the reductive amination of aldehydes with
anilines to provide secondary amines and tertiary amines in good yields. The
method is highly chemoselective and tolerates a wide range of functional groups,
such as NO2, CN, CO2Me, F, Cl, Br, OMe, Me, furyl and
alkyl.
B. Li, J. Zheng, W. Zeng, Y. Li, L. Chen, Synthesis, 2017,
49, 1349-1355.
A Chan-Lam coupling reaction of benzylic and allylic boronic esters
with primary and secondary anilines provides valuable alkyl amine products. Both
secondary and tertiary boronic esters can be used as coupling partners, with
mono-alkylation of the aniline occurring selectively.
J. D. Grayson, F. M. Dennis, C. C. Robertson, B. M. Partridge, J. Org. Chem., 2021, 86,
9883-9897.
Dibutyltin dichloride catalyzes a direct reductive amination of aldehydes and
ketones in the presence of phenylsilane as a stoichiometric reductant. Suitable
amines included anilines and dialkylamines but not monoalkylamines.
R. Apodaca, W. Xiao,
Org. Lett., 2001, 3, 1745-1748.
A simple copper-promoted N-monoalkylation of anilines that utilizes alkyl
boronic acids as the alkylating partner is carried out in refluxing dioxane and
allows a number of structurally and electronically diverse anilines to be
functionalized in a single step. A broad study was carried out to demonstrate
the utility of this new methodology for the preparation of phenethylanilines.
M. Larrosa, C. Guerrero, R. Rodríguez, J. Cruces, Synlett, 2010,
2101-2105.
A CuI-based catalytic system in combination
with an easily accessible prolinamide ligand enables an Ullmann-type cross coupling of a variety of aromatic, aliphatic amines
with aryl halides in aqueous media. The method is mild and tolerates air and a wide range of functional groups. Secondary amines
like heteroaromatic amines and nucleobases afford the
corresponding coupling products in good to excellent yields too.
G. Chakraborti, S. Paladhi, T. Mandal, J. Dash, J. Org. Chem., 2018, 83,
7347-7359.
The use of in situ generated magnesium amides in the presence of a lithium
halide dramatically increases the product yield of iron-catalyzed amination
reactions. The present method is simple and free of precious and expensive
metals and ligands and provides a convenient route to triarylamines, a recurrent
core unit in organic electronic materials as well as pharmaceuticals.
T. Hatakeyama, R. Imayoshi, Y. Yoshimoto, S. K. Ghorai, M. Jin, H. Takaya, K.
Norisuye, Y. Sohrin, M. Nakamura, J. Am. Chem. Soc., 2012,
134, 20262-20265.
In the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) as an
additive, easily prepared and handled N-chloroamines react with aryl
Grignard reagents to give various arylamines in good to excellent yields.
Functional groups such as ester and nitrile are tolerated.
T. Hatakeyama, Y. Yoshimoto, S. K. Ghorai, M. Nakamura, Org. Lett., 2010,
12, 1516-1519.
A rhodium-catalyzed amination reaction of aryl halides with amines takes place
in the presence of a N-heterocyclic carbene ligand. The active metal
species responsible for the reaction progress was identified. This convenient
and mild procedure for Rh-catalyzed N-arylation displays a wide range of
substrate scope and high degree of functional group tolerance.
M. Kim, S. Chang, Org. Lett., 2010,
12, 1640-1643.
A molybdenum-mediated reductive hydroamination of vinylcyclopropanes with
nitroarenes provides substituted homoallylamines were prepared in very good
yields. No noble metal catalysts were used in this reaction, and Mo(CO)6
acted as both catalyst and reductant. This protocol provides an effective method
for the selective synthesis of substituted homoallylamines from easily available
nitroarenes.
J.-L. Lu, Z. Zhang, J.-T. Deng, A.-J. Ma, J.-B. Peng, Org. Lett., 2023, 25,
2991-2995.
A transition-metal-free synthesis of aryl- and heteroarylamines employs a small-ring
organophosphorus-based catalyst and a terminal hydrosilane reductant to drive reductive intermolecular
coupling of nitroarenes with boronic acids. Applications to the
construction of both Csp2-N (from arylboronic acids) and Csp3-N bonds (from
alkylboronic acids) are demonstrated; the reaction is stereospecific with
respect to Csp3-N bond formation.
T. V. Nykaza, J. C. Cooper, G. Li, N. Mahieu, A. Ramirez, M. R. Luzung, A. T.
Radosevich, J. Am. Chem. Soc.,
2018,
140, 15200-15205.
A low-valent tungsten complex catalyzes a visible light mediated amination of
boronic acids with nitroaromatics at ambient temperature. With readily available
W(CO)6 as a precatalyst under external-photosensitizer-free
conditions, nitroaromatics smoothly undergo C-N coupling reactions with boronic
acids, delivering structurally diverse secondary amines in good yields.
H. Song, Y. Shen, H. Zhou, D. Ding, F. Yang, Y. Wang, C. Xu, X. Cai, J. Org. Chem., 2022, 87,
5303-5314.
Palladium/N-heterocyclic carbene (NHC) catalysis achieves an amination of
diaryl sulfoxides with anilines and alkylamines. This amination tolerates a wide
range of functional groups such as silyl, boryl, methylsulfanyl, and halogen
moieties. Regioselective amination of unsymmetrical diaryl sulfoxides was also
executed by means of steric bias.
Y. Yoshida, S. Otsuka, K. Nogi, H. Yorimitsu, Org. Lett.,
2018, 20, 1134-1137.
Various aromatic amines expediently underwent a copper-catalyzed N-tert-butylation
in the presence of tert-butyl 2,2,2-trichloroacetimidate at room
temperature.
J. W. Cran, D. V. Vidhani, M. E. Krafft,
Synlett, 2014, 25, 1550-1554.
The sequential combination of Ti-catalyzed hydroamination of alkynes followed
by the Ti-catalyzed hydrosilylation of the intermediate imines is an efficient
one-pot process for the conversion of alkynes and primary amines into secondary
amines.
A. Heutling, F. Pohlki, I. Bytschkov, S. Doye, Angew. Chem. Int. Ed., 2005,
44, 2951-2954.
1,2,3-triazole-bound cationic Au(I) catalysts possess much better thermal
stability than literature-reported Au catalysts, including IPrAu•NTf2.
By application of these catalysts, challenging intermolecular hydroaminations
were achieved with less-reactive internal alkynes and unprotected aliphatic
amines, giving excellent yields with low catalyst loading.
H. Duan, S. Sengupta, J. L. Petersen, N. G. Akhmedov, X. Shi, J. Am. Chem. Soc., 2009,
131, 12100-12102.
An efficient intermolecular hydroamination of unactivated alkenes with anilines
catalyzed by lanthanide salts gives Markovnikov products in good yields.
P. Yin, T.-P. Loh, Org. Lett., 2009,
11, 3791-3793.
N-Alkylaminobenzenes
were prepared in a simple and efficient one-pot synthesis by reduction of
nitrobenzenes followed by reductive amination with decaborane (B10H14)
in the presence of 10% Pd/C.
J. W. Bae, Y. J. Cho,
S. H. Lee, C.-O. M. Yoon, C. M. Yoon, Chem. Commun., 2000,
1857-1858.
Cooperative catalysis of an Ir(III)-diamine complex and a chiral phosphoric
acid or its conjugate base enables a direct reductive amination of a wide range
of ketones.
C. Li, B. Villa-Marcos, J. Xiao, J. Am. Chem. Soc., 2009,
131, 6967-6969.
The NiCl2(PPh3)2-PPh3-catalyzed cross-coupling of bromomagnesium diarylamides, generated in situ from
diarylamines, with aryl bromides or iodides is an inexpensive, convenient, and practical method
for the synthesis of triarylamines.
C. Chen, L.-M. Yang, Org. Lett., 2005,
7, 2209-2211.
Air- and moisture-stable Ni(II)-(σ-aryl) complexes, associated with N-heterocyclic
carbene ligands, produce a catalytically active Ni(0) species in situ for an
efficient amination of aryl chlorides with anilines and secondary cyclic amines
under mild conditions.
C. Chen, L-M. Yang, J. Org. Chem., 2007,
72, 6324-6327.
A base-mediated hydroamination protocol with substoichiometric amounts of a
hydrosilane and potassium tert-butoxide operates under mild conditions.
Many aryl- and heteroatom-substituted olefins as well as arylamines are
tolerated, affording the desired products with complete regioselectivity.
P. Li, B. C. Lee, X. Zhang, M. J. Koh, Synthesis, 2022, 54,
1566-1576.
A cobalt-catalyzed highly branched- and enantioselective allylic amination of
racemic branched allylic carbonates bearing alkyl groups with both aromatic and
aliphatic amines provides allylic amines in high yields with exclusively
branched selectivity and excellent enantioselectivities under mild reaction
conditions.
S. Ghorai, S. S. Chirke, W.-B. Xu, J.-F. Chen, C. Li, J. Am. Chem. Soc.,
2019,
141, 11430-11434.
A rhodium-catalyzed regioselective amination of secondary allylic
trichloroacetimidates with unactivated aromatic amines gives N-arylamines
in high yields and regioselectivity, favoring the branched amination products.
The presence of the trichloroacetimidate leaving group was found to be critical
for successful regioselective amination reactions with unactivated aromatic
amines.
J. S. Arnold, R. F. Stone, H. M. Nguyen, Org. Lett., 2010,
12, 4580-4583.
A ligand-free copper-catalyzed hydroamination of allenes with cyclic secondary
amines or anilines derivatives provides (E)-allylamines under smooth
conditions with total regio- and stereoselectivity.
R. Blieck, J. Bahri, M. Taillefer, F. Monnier, Org. Lett., 2016, 18,
1482-1485.
A rhodium-catalyzed regioselective amination of tertiary allylic
trichloroacetimidates with unactivated aromatic amines is a direct and efficient
approach to the preparation of α,α-disubstituted allylic aryl amines in good
yield and with excellent regioselectivity. This method enables the conversion of
unactivated primary and secondary amines and the preparation of reverse
prenylated indoles in two steps.
J. S. Arnold, G. T. Cizio, H. M. Nguyen, Org. Lett., 2011,
13, 5576-5579.
Various allyl carbonates have been converted under Fe catalysis into
essentially regio- and stereoisomerically pure allyl amines. Catalytic
amounts of piperidinium hydrochloride as a buffer retard catalyst
decomposition.
B. Plietker, Angew. Chem. Int. Ed., 2006,
45, 6053-6056.
p-Toluenesulfonic acid efficiently catalyzes direct
nucleophilic substitutions of the hydroxy groups of propargylic alcohols with a
large variety of carbon- and heteroatom-centered nucleophiles. Reactions can be
conducted under mild conditions and in air without the need for dried
solvents.
R. Sanz, A. Martinez, J. M. Alvarez-Gutierrez, F. Rodriquez, Eur. J. Org. Chem., 2006,
1383-1386.
A direct Fe-catalyzed synthesis of β-alkyl N-aryl aza Baylis-Hillman
(ABH) adducts involves the formation of a C–N bond via a nitroso-ene reaction.
This is a simple, fast, and best alternate method to overcome the substrate
scope limitations of the ABH reaction. Various arylhydroxylamines reacted with
esters, aldehydes, ketone, and nitriles to yield the corresponding products in
good yields.
S. Murru, A. A. Gallo, R. S. Srivastava, J. Org. Chem., 2012,
77, 7119-7123.
A palladium-catalyzed allylic amination enables an asymmetric synthesis of
α,α-disubstituted allylic N-arylamines from highly modular vinyl cyclic
carbonates and unactivated aromatic amine nucleophiles. The catalytic process
features minimal waste production, high asymmetric induction, and operational
simplicity.
A. Cai, W. Guo, L. Martínez-Rodríguez, A. W. Kleij, J. Am. Chem. Soc., 2016,
138, 14194-14197.
A regio- and enantioselective amination of racemic tertiary allylic
trichloroacetimidates with a variety of aniline nucleophiles in the presence of
a chiral diene-ligated rhodium catalyst is a direct and efficient route to
chiral α,α-disubstituted allylic N-arylamines in good yields with very
good levels of regio- and enantioselectivity.
J. S. Arnold, H. M. Nguyen, J. Am. Chem. Soc., 2012,
134, 8380-8383.
An efficient and very simple conjugate addition of aromatic and aliphatic
amines to α,β-unsaturated carbonyl compounds under solvent-free conditions in
the presence of catalytic amount of silicon tetrachloride gave the corresponding
Michael adducts with very good yields.
N. Azizi, R. Baghi, H. Ghafuri, M. Boloutchian, M. Hashemi, Synlett, 2010,
379-382.
Heating a solution of an aldehyde, an aromatic amine, and a nitroalkane in 20%
water-methanol at 60 °C for five hours enables an environmentally
three-component, one-pot synthesis of 2-nitroamines in the absence of a catalyst.
C. G. Piscopo, G. Sartori, J. A. Mayoral, D. Lanari, L. Vaccaro, R. Maggi, Synlett, 2013, 24,
2596-2600.